1. Field of the Invention
The invention relates to improved supports for the base plates of an annealing furnace upon which coils to be annealed are placed, and more particularly to such base plate supports for use in annealing furnaces of the type taught in U.S. Pat. No. 3,588,305.
2. Description of the Prior Art
While not intended to be so limited, the base plate supports of the present invention are particularly adapted for use in annealing furnaces of the type taught in U.S. Pat. No. 3,588,305 and, for purposes of an exemplary showing, will be described in association with such an annealing furnace. Annealing furnaces of this type may be used for various purposes. They are well suited, for example, for practicing the final anneal on oriented silicon iron for magnetic uses, during which the desired orientation is achieved. Such furnaces are adapted to operate both under a vacuum and under a desired annealing atmosphere. For an exemplary teaching of a process of annealing oriented silicon iron for magnetic purposes in such furnaces, reference is made to the copending application Ser. No. 609,189, filed Sept. 2, 1975 in the name of the same inventors and entitled A METHOD OF ANNEALING ORIENTED SILICON STEEL.
As will be described more fully hereinafter, the bottom of the heating chamber of a furnace of this type comprises a wheeled car adapted to ride upon rails or other appropriate surfaces. The coils to be annealed may be placed upon the car and the car rolled into the outer shell of the furnace. In general, the car also carries the front insulative wall of the heating chamber within the furnace shell, so that when the car is in position within the furnace shell, it completes the insulative heating chamber, fully enclosing the coils.
Depending upon the size of the furnace, the car bottom of the heating chamber is adapted to carry one or more coils. The upper surface of the car is covered with an appropriate refractory ceramic fiber. Spaced upwardly of the refractory ceramic fiber there is a base plate for each coil, each coil being placed upon its respective base plate. Between the bottom of each base plate and the upper surface of the car there is located an electrical heating element of molybdenum or other appropriate material. This heating element is, itself, appropriately supported on insulative means. When the car is fully located within the furnace outer shell, the heating elements are manually connected to the electrical facilities of the furnace so that they may be turned on and turned off at desired times during the annealing procedure.
Heretofore, the base plates have been supported in horizontal position, spaced upwardly from the refractory ceramic fiber covering the upper surface of the car by a series of approximately nine hollow stainless steel posts. Each post extended up through the refractory ceramic fiber on the car top and had a length of approximately 14 inches, an external diameter of approximately 5 inches and an internal diameter of about 2 inches. The lowermost end of each post was reduced in diameter and adapted to be received in a socket formed on the upper surface of the car. Both the socket bottom and the hollow center of the post were filled with insulative material to prevent the posts and the car to which they were affixed from acting as a heat sink for the base plate.
In recent years it has become the practice to anneal large coils of silicon steel weighing in the neighborhood of from 30,000 to 40,000 pounds. During the annealing process, temperatures of 2,200.degree.F or more are reached. Despite the fact that the base plates comprise disc-like stainless steel or ingot iron members having a thickness of approximately 6 inches and a diameter in excess of 80 inches, it has been found that by virtue of the high temperatures during the annealing procedure and the great weight supported by the base plates, the base plates have shown a tendency to become permanently warped and distorted due to the inadequacy of the prior art support means for them. Distortion and warpage of the base plates has resulted in distortion of the coils mounted on them, seriously impairing the final product.
The present invention is directed to the provision of improved supports for the base plates. While blocks of stainless steel, ingot iron and the like were substituted for the prior art posts, it was found that such blocks would expand during heat-up and would ultimately deform so that they would not contract to their original shape. The present invention is based upon the discovery that support means in the form of blocks of appropriate refractory material would overcome the various problems encountered with the prior art posts, as enumerated above. The refractory blocks of the present invention are so arranged as to provide maximum support for the base plates, while at the same time permitting adequate circulation of atmosphere about the heating elements beneath the base plates.